/Engine/Source/Runtime/AudioMixer/Public/AudioMixerSubmix.h
Add (if not already added) or sets the amount of the source voice's send amount.
void AddOrSetSourceVoice ( FMixerSourceVoice * InSourceVoice, const float SendLevel, [EMixerSourceSubmixSendStage](API\Runtime\AudioMixer\Audio__EMixerSourceSubmixSendSta-) InSubmixSendStage )